A carbonate diester (e.g., dialkyl carbonate, dicycloalkyl carbonate, or diaralkyl carbonate) is utilized in industry for producing a therapeutically active compound or an agricultural chemical or producing polycarbonate or polyurethane. Heretofore, the carbonate diester has been prepared by causing a reaction between phosgene and an alcohol. This process, however, has disadvantages in that the toxic phosgene is necessarily employed as the starting compound and a corrosive hydrogen chloride is produced. A process for the preparation of a carbonic diester using no phosgene has already been developed. This process comprises a liquid-phase reaction between carbon monoxide and an alcohol in the presence of a copper halide catalyst or a palladium chloride catalyst. This process also has disadvantageous features in that carbon dioxide which is produced as by-product lowers selectivity on the carbon monoxide basis, and water which is also produced as by-product, makes it difficult to recover the yielded carbonate diester from the reaction mixture. Moreover, since the reaction is conducted in a liquid phase, it becomes necessary to separate the yielded carbonate diester from the catalyst. Therefore, this process appears unfavorable from the viewpoint of production of a carbonate diester in industry.
Japanese Patent Provisional Publication No. 60-181051 discloses a process for preparing a carbonate diester (i.e., diester of carbonic acid) in a gaseous phase by reacting carbon monoxide and a nitrite ester in the presence of a solid platinum group metal catalyst or a platinum group metal compound supported by a carrier using an oxidizing agent containing O.sub.2 in an amount of 10 molar % per carbon monoxide. This process has a problem in that an oxalic acid diester, that is a by-product, is also produced not a small amount.
Japanese Patent Provisional Publications Nos. H3-141243 and H4-139152 disclose a process for preparing dimethyl carbonate by catalytic reaction between carbon monoxide and methyl nitrite in a gaseous phase in the presence of a catalytic composition which comprises a carrier such as active carbon or alumina and a catalytic element comprising a compound of metal of the platinum group such as palladium chloride or palladium sulfate and a compound of metal such as iron, copper, bismuth, cobalt, nickel, or tin.
Japanese Patent Provisional Publication No. H4-89458 describes that employment of a small amount of hydrogen chloride in the above-mentioned process for the production of dimethyl carbonate using the catalyst composition which comprises a carrier such as active carbon or alumina and a catalytic element comprising a compound of metal of the platinum group and a compound of iron or the like is effective for keeping the activity of catalyst at a high level for a prolonged period of time.
EP-A-0 523 508 describes a process for producing a dialkyl carbonate by catalytic reaction from carbon monoxide and an alkyl nitrite in a gaseous phase in the presence of a halide of a metal of the platinum group or a complex compound containing a halide of a metal of the platinum group which is supported by a carrier of aluminum oxide, hydroxide of aluminum oxide, or aluminum hydroxide having a large specific surface area.
EP-464460B1 describes a process for producing a dialkyl carbonate by catalytic reaction between carbon monoxide and an alkyl nitrite in a gaseous phase which employs a catalyst comprising a carrier and a halide of a metal of the platinum group or a complex compound containing a halide of a metal of the platinum group which is modified by an element such as iron, cobalt, nickel or copper. The working examples described therein all employ alumina (i.e., aluminum oxide). The publication further has a description in that carriers which are generally employed for supporting a catalyst of the platinum group metal such as spinel, silicate, montmorillonite, zeolite, active carbon, molecular sieves, diatomaceous earth, silicon carbide, and silicon dioxide can be used.